Open Circuit Fault Control Techniques for Bearingless Multi-Sector Permanent Magnet Synchronous Machines

This article presents three-phase and single-phase open-circuit fault-tolerant control strategies of radial suspension force and torque generation for bearingless multisector surface mounted permanent magnet synchronous machines. A combined winding topology is installed in the stator so that each phase contributes to both suspension force and motoring torque production. Indeed, a triple sectored three-phase winding is employed. Each three-phase winding is supplied by a power converter to independently control the suspension force vector and torque over each sector. An analytical formulation of the force and torque generation is described considering both three-phase open-circuit and single-phase open-circuit fault conditions. The analytical models of the machine are presented in a generalized matrix form so that they can be applied to any machine with a multisector winding structure. The analytical models are then used to derive the control algorithms that allow us to control the bearingless machine when a whole three-phase winding or one phase of one or two sectors are open circuited. The theoretical analysis is verified with both finite elements analysis and experiment tests. This system shows a good open-circuit fault-tolerant capability.